(1) Field of the Invention
The present invention relates to the field of Chemical Mechanical Polishing (CMP). More particularly, the present invention relates to methods and apparatus for chemical mechanical polishing of substrates, such as semiconductor substrates, on a rotating polishing pad in the presence of chemically and/or physically abrasive slurry. The present invention provides a pad profile conditioning apparatus to condition the polishing pad while the polishing pad is being used to polish semiconductor substrates.
(2) Description of the Prior Art
Chemical Mechanical Polishing is a method of polishing materials, such as semiconductor substrates, to a high degree of planarity and uniformity. The process is used to planarize semiconductor slices prior to the fabrication of semiconductor circuitry thereon, and is also used to remove high elevation features created during the fabrication of the microelectronic circuitry on the substrate. One typical chemical mechanical polishing process uses a large polishing pad that is located on a rotating platen against which a substrate is positioned for polishing, and a positioning member which positions and biases the substrate on the rotating polishing pad. Chemical slurry, which may also include abrasive materials therein, is maintained on the polishing pad to modify the polishing characteristics of the polishing pad in order to enhance the polishing of the substrate.
The use of chemical mechanical polishing to planarize semiconductor substrates has not met with universal acceptance, particularly where the process is used to remove high elevation features created during the fabrication of microelectronic circuitry on the substrate. One primary problem which has limited the used of chemical mechanical polishing in the semiconductor industry is the limited ability to predict, much less control, the rate and uniformity at which the process will remove material from the substrate. As a result, CMP is a labor intensive process because the thickness and uniformity of the substrate must be constantly monitored to prevent overpolishing or inconsistent polishing of the substrate surface.
The profile of the polishing pad plays an important role in determining good overall polishing results. The polishing pad can, for instance, be profiled thick at the inner diameter of the polishing pad as compared to the outer diameter of the polishing pad and visa versa. The profile of the polishing pad is typically achieved by trial and error and by adjusting the position of a diamond dresser (see following paragraph). This method of profiling the polishing pad is destructive, time consuming and causes the loss of the polishing pad. Since this measure of the polishing pad profile can only be performed at the end of the useful life of the polishing pad, the wrong profile can only be detected after the polishing pad has served its useful life.
The function of the diamond dresser is to maintain and/or restore the polishing characteristics of the polishing pad to the maximum extent possible during the polishing operation and in doing so to extend the useful life or the operating characteristics of the polishing pad. The diamond dresser performs this function by influencing the polishing action of the polishing pad during its operation. This influencing can take the form of exerting pressure on the polishing pad and in so doing influencing the polishing characteristics of the polishing pad.
The polishing process is carried out until the surface of the wafer is ground to a highly planar state. During the polishing process, both the wafer surface and the polishing pad become abraded. After numerous wafers have been polished, the polishing pad becomes worn to the point where the efficiency of the polishing process is diminished and the rate of removal of material from the wafer surface is significantly decreased. It is usually at this point that the polishing pad is treated and restored to its initial state so that a high rate of uniform polishing can once again be obtained.
FIG. 1 shows a Prior Art CMP apparatus. A polishing pad 20 is affixed to a circular polishing table 22 that rotates in a direction indicated by arrow 24 at a rate in the order of 1 to 100 RPM. A wafer carrier 26 is used to hold wafer 18 face down against the polishing pad 20. The wafer 18 is held in place by applying a vacuum to the backside of the wafer (not shown). The wafer 18 can also be attached to the wafer carrier 26 by the application of a substrate attachment film (not shown) to the lower surface of the wafer carrier 26. The wafer carrier 26 also rotates as indicated by arrow 32, usually in the same direction as the polishing table 22, at a rate on the order of 1 to 100 RPM. Due to the rotation of the polishing table 22, the wafer 18 traverses a circular polishing path over the polishing pad 20. A force 28 is also applied in the downward vertical direction against wafer 18 and presses the wafer 18 against the polishing pad 20 as it is being polished. The force 28 is typically in the order of 0 to 15 pounds per square inch and is applied by means of a shaft 30 that is attached to the back of wafer carrier 26.
Accordingly, the subject surface (that is the lower surface) of the substrate 18 is polished by the combination of a chemical polishing action of alkali contained in the polishing agent or slurry 21 and a mechanical polishing action by silica contained in the polishing slurry 21.
U.S. Pat. No. 5,775,983 (Shendon et al.) shows a conical roller for conditioning a pad.
U.S. Pat. No. 5,779,526 (Gill) show a polishing pad conditioning roller.
U.S. Pat. No. 5,681,212 (Hayakawa) shows a disk dresser.
U.S. Pat. No. 5,421,768 (Fijiwara et al.) shows a brush to clean a polishing pad.
U.S. Pat. No. 5,688,360 (Jairath) shows cylindrical and conical polishing pads.